1. What is the expected reading obtained on a Digital Display Meter with diode-checking function when a proper functioning silicon semiconductor diode is connected across its leads in the reverse bias configuration?
a) 0.67 V
b) 0.3 V
c) Open Loop Indication
d) Varies with the diode
Explanation: The diode checking function on the meter when used causes a current of 2 mA to flow through the diode and hence under reverse bias, the result obtained is the open loop indication.
2. A diode on being checked by a DDM with diode checking function results in an open loop indication in both directions. Which of the following is the correct inference drawn from the given situation?
a) Power failure to the DDM
b) Diode is faulty
c) Diode is proper
d) Device isn’t connected properly
Explanation: . A diode allows electrical conduction in just one direction. Hence, if an instrument shows an open loop indication in both the directions, then the diode is faulty.
3. A silicon semiconductor diode when subjected to ohmmeter testing gives low resistance in both directions. Which of the following is the correct inference to be drawn?
a) Diode is faulty
b) Power failure to the Ohmmeter
c) Diode is short-circuited
d) Diode is open circuited
Explanation: A proper diode gives a low resistance reading along one direction and high resistance reading along the other. Hence, if diode gives low resistance readings in both directions, then the diode must be short-circuited. It’s noteworthy that a faulty diode gives a high resistance reading along both paths.
4. A silicon semiconductor diode when subjected to ohmmeter testing gives high resistance in both directions. Which of the following is the correct inference to be drawn?
a) Diode is faulty
b) Power failure to the Ohmmeter
c) Diode is short-circuited
d) Diode is open circuited
Explanation: A proper diode gives a low resistance reading along one direction and high resistance reading along the other. Hence, if diode gives high resistance readings in both directions, then the diode must be faulty.
5. How can the location of the Zener region be controlled in the diode characteristic curve?
a) By changing the value of Iz
b) By changing the doping concentration of the diode
c) By changing the operating temperature
d) By increasing the size of diode
Explanation: An increase in doping will lead to an increase in the concentration of impurities, which would further lead to a change in VZ and hence change in the Zener region.
6. Which material is generally used for the manufacture of Zener diode?
a) Silicon
b) Germanium
c) Mercury
d) Arsenic
Explanation: Because of its high heat and current handling capacity, Silicon is generally used for the manufacture of Zener diodes.
7. Which of the following is not a part of the equivalent circuit of a Zener diode?
a) Dynamic Resistance
b) DC Battery
c) Ideal diode
d) Piecewise linear model of diode
Explanation: The equivalent circuit diagram of a Zener diode doesn’t involve an ideal diode as it is used under reverse bias and an ideal diode doesn’t conduct under reverse bias.
8. At 298 K, the nominal Zener voltage is found to be equal to 10 V. Given that the value of the temperature coefficient is 0.072 (%/K), what is the nominal Zener Voltage at 398 K?
a) 9.46 V
b) 9.54 V
c) 0.54 V
d) 10.54 V
Explanation: The change in VZ with temperature is calculated from the following equation:
Change in VZ = TC.VZ(T1 – T0))/1000
Change in VZ = 0.54 V
Now, as the value of TC is positive, new VZ = 10 + 0.54 V = 10.54 V.
9. Which of the following materials is used to make LEDs?
a) Silicon
b) GaAsP
c) Germanium
d) Selenium
Explanation: In Silicon and Germanium, the major chunk of energy is given off as heat the hence the emitted light isn’t significant. In Gallium Arsenide Phosphide (GaAsP), the number of photons are enough to create a visual source of light.
10. Which of the following voltages may be considered as a safe and sufficient voltage for the operation of a LED?
a) 0.7 V
b) 5 V
c) 2.7 V
d) -5 V
Explanation: The safe and sufficient operating voltage range for LED is between 1.7 V to 3.3 V. Hence, 2.7 V is the best option.